Pump

Abstract: A dual chamber pump comprises a shaft (20) to each end of which is attached a driven member (30), a body member (45) being disposed over each driven member (30) to define therewith a pumping chamber (70), to which chambers (70) is alternately fed a supply of pressure. The driven members (30) each includes an expandable bellows (36) which reduces wear on the pump, while it is preferred that the body members (45) are secured to the pump by rotatable body rings (18) which enable ready disassembly of the pump by rotation of the body rings (18).

Description: The present invention relates to a pump with the features of the preamble of Claims 1 and 2, and more particularly to a simple and compact design for a reciprocating, dual chamber, compressed air driven pump. The strength of the pump's design facilitates making the pump entirely of corrosion resistant materials. Dual chamber diaphragm pumps are known in the art. Pumps of this type are described in U.S. Patent No. 4,708,601 to Bazan et al, U.S. Patent No. 4,817,503 to Yamada, and U.S. Patent No. 5,108,270 to Kozumplik, Jr. The pumps disclosed in these patents are pumps in which air pressure drives a pair of flexible diaphragms. Each diaphragm draws fluid through an inlet into a pumping chamber and forces the fluid out through an outlet as the diaphragm moves back and forth inside the pump. Such pumps have found widespread use pumping a diverse variety of fluids including water, chemicals, food products and other materials. Known diaphragm pumps often have complicated designs including small metal fittings and fasteners. These complicated designs hinder disassembly and reassembly of the pumps. This makes routine maintenance and overhaul somewhat difficult. It would be desirable, therefore, to provide an improved pump design that would require less frequent maintenance. It would be further desirable to provide a simpler pump design allowing for convenient disassembly and reassembly to make required maintenance easier to perform. Some dual chamber diaphragm pumps are adapted to pump corrosive fluids. These fluids would attack and corrode the metal parts commonly used in pumps designed for less demanding applications. In these pumps, some or all of the parts that normally come into contact with the pumped material (the wetted parts) are formed of or coated with chemically inert materials. United States Patent Numbers 4,817,503 and 5,108,270 (mentioned above), as well as U.S. Patent No. 4,867,653 to Mills et al, describe pumps having some parts formed of corrosion resistant materials. However, even those pumps whose wetted parts are formed of or coated with corrosion resistant materials almost invariably include some metal parts in other, exterior locations. In many cases metal parts are used as fasteners and fittings to hold the pump bodies and associated tubing together. This is presumably because metal parts are significantly stronger and more easily machined than are corrosion resistant parts, which are typically made of some type of soft (relative to metal) plastic. Pumps having exposed metal parts only in exterior locations not normally contacted by the pumped fluids are acceptable in many applications. However, such pumps have proven problematic in semiconductor manufacturing applications. These applications are doubly demanding in that extreme purity must be maintained in highly corrosive chemicals including a range of solvents and acids. No matter how much care is used, it is virtually impossible to completely prevent leakage from a pump in a manufacturing operation. Small quantities of leaked chemicals will eventually contact the exposed fasteners and other metal parts of known pumps. When this occurs, the metal parts corrode and the dissolved corrosion products may leach back into the pump and contaminate the system. In most applications this is not critical--the contaminant quantities are relatively small and ultrapure chemicals are not absolutely essential. In semiconductor manufacturing, however, even tiny amounts of contamination may be disastrous. Currently, electronic components are fabricated by the millions on single silicon chips and those chips are manufactured in large numbers in automated production runs. Chip failures due to contamination are not typically detected until the individual chips are tested after the manufacturing operation is complete. Under these circumstances, a single source of corroded metal leaking back into the fluid system may cause the loss of many thousands of dollars worth of product. Furthermore, expensive delays occur while the production line is shut down until the source of contamination can be located and the system purged. WO-A-84/04363 discloses a dual chamber bellows pump the body and bellows of which are formed of PTFE. However the pump further includes components of metal, while the valves of the pump include magnets. In order to attempt to avoid corrosion of the metallic parts, they are encased within a PTFE structure. However, with such an arrangement, there is still leakage of corrosive media into contact with metallic parts, resulting in contamination leaking back into the media. EP-A-0 410 394, on which the preamble of Claim 1 is based, describes a pneumatically operated bellows pump the bellows of which are made of a plastics material and are fitted with metal flanges and screws. The remainder of the pump is of conventional construction incorporating both metal and plastics parts. In order to attempt to prevent corrosion of the metal parts of the pump and contamination of the media being pumped, leak detectors are incorporated in the pump and are arranged to shut down the pump when leakage is detected. DE-A-2542 392, on which the preamble of Claim 2 is based, discloses a dual chamber diaphragm pump operating on a principle of rotation and incorporating an eccentric cam arrangement for alternating pump chambers, said eccentric cam arrangement being metallic. Additionally, the pump further includes metallic bayonet locking rings opening and closing of which requires the use of a heavy hammer or a hydraulic jack. It would be desirable to be able to provide a dual chamber pump which overcomes the disadvantages of the aforementioned arrangements, and in particular the problems associated with corrosion of the metal components and contamination of the fluid being pumped. According to one aspect of the present invention, there is provided a pump comprising a pump shaft, a pair of driven members secured one to each end of the shaft, a pair of body members disposed over the driven members and each having an interior which, in combination with the associated driven member, defines a pumping chamber, and means for applying pressure alternately to the driven members, each driven member includes an expandable bellows, characterised in that the pump is formed entirely of corrosion resistant plastics. The use of expandable bellows increases the volume of fluid pumped on each stroke and the pumping frequency can be reduced accordingly. This significantly decreases wear on the bellows, internal seals and other parts of the pump. Service intervals are thereby lengthened considerably in comparison with dual chamber diaphragm pumps previously known. Additionally, in fluid pumped by a bellows pump, the pressure pulsations are of lower frequency and amplitude than in fluid pumped by a diaphragm pump. Additionally, the fact that the pump is formed entirely of corrosion resistant plastics means that it can be used in particularly demanding applications - such as those encountered in the semi-conductor industry - where the purity of highly corrosive materials must be strictly maintained. According to a further aspect of the present invention, there is provided a pump comprising a pump core, a pump shaft, a pair of driven members secured one to each end of the shaft, a pair of body members disposed over the driven members and each having an interior which, in combination with the associated driven member, defines a pumping chamber, means for applying pressure alternately to the driven members, and a pair of body rings in connection with said pump core and rotatable between locked and unlocked positions, one securing each of the body members to the pump whereby said body members are manually releasable from the pump, without tools, by rotation of the associated body rings, characterised in that the pump is entirely constructed of corrosion resistant plastics. Although this design may find use in pumps using flexible diaphragms as driven members, preferred embodiments will use the pair of expandable bellows referred to above. Preferably inlet and outlet tubes for the flow of pumped fluid are secured to the pump by sets of rotatable tube locking rings. The simplicity of the design is advantageous in that the pump is easy to disassemble and reassemble for inspection, cleaning or maintenance. Additionally, the pump, being made entirely of corrosion resistant plastic such as organic polymers, is particularly suited to demanding applications - such as those encountered in the semi-conductor industry - in which pumps are used with highly corrosive materials whose purity must be strictly maintained. By way of examples only, the aspects of the invention will now be described in greater detail with reference to the accompanying drawings of which: Figure 1 is an exploded view showing a pump constructed according to the present invention; and Figure 2 is a side sectional view showing the interior of the pump. Referring to the drawings, and as can be seen in Fig. 1, pump 10 is generally symmetrical with equivalent parts assembled on each side of a central pump core 15. For clarity, the assembly of only one side of the pump will be described; it should be understood that the other side is substantially equivalent. Understanding of the pump's construction will be aided by frequent cross referencing to Fig. 2. As is customary, equivalent parts are given the same reference numbers in both views. Referring principally to Fig. 1, pump 10 is assembled around pump core 15. A rotatable body ring 18 is held in place against the pump core by a back plate 25. Back plate 25 is fixed to the pump core by plastic screws (not shown), which pass through the back plate into the pump core. The body ring is rotatable about a central axis passing through the pump core. A pump shaft 20 is slidably disposed through pump core 15. Pump shaft 20 slides through four small O-rings 22 (Fig. 2), which provide a seal between the shaft and pump core 15. It should be understood that pump shaft 20 is in reality smooth along its length so that a positive seal is maintained between the shaft and O-rings 22 (Fig. 2). Pump shaft 20 also extends through back plate 25. Back plate 25 will form a back surface for an air pressure chamber as will be described further below. The ends 27 of pump shaft 20 are typically of larger diameter than the rest of the shaft as seen in Fig. 2. The left end 27 of pump shaft 20 can also be glimpsed on the left side of the pump in Fig. 1. Again, the parallel lines on the end of the shaft in Fig. 1 are an artifact of the drawing program used to prepare Fig. 1. In reality, the ends 27 of pump shaft 20 are provided with external threads 28 (Fig. 2) for engagement with driven members 30. The driven members can be seen in both Fig. 1 and Fig. 2. Driven member 30 is a generally cup-shaped body comprising an end cap 32 (Fig. 1) and a flange-shaped base 34 joined by an expandable bellows 36. The base 34 of driven member 30 is held against back plate 25 as will be described further below. A seal is maintained between the driven member and the back plate by an O-ring 38. In combination, back plate 25 and the interior of driven member 30 define a pressure chamber 40 (Fig. 2) in which air pressure drives the expansion of bellows 36. The end caps 32 of driven members 30 are fixed to pump shaft 20 by means of a threaded connection 28 (Fig. 2) at the ends 27 of the shaft. The base 34 of each driven member 30 is secured to pump core 15. As the expandable bellows 36 of one driven member 30 expands, the other bellows is pulled into compression by pump shaft 20. In Fig. 1 and Fig. 2, the expandable bellows on the left side of the pump is shown expanded while the expandable bellows on the right side of the pump is shown compressed. A pump body member 45 fits over driven member 30 with a seal maintained between them by O-ring 47, which can be seen in Fig. 2 and on the left side of the pump in Fig. 1. As can best be seen in Fig. 1, pump body member 45 comprises a dome 48 and a base 49. External threads (not shown) around the rim of the base engage with internal threads on body ring 18. Rotation of the body ring firmly secures base 49 of body member 45 over the flange-shaped base 34 of driven member 30. Thus, body member 45 and driven member 30 are both secured to the pump by body ring 18. When maintenance or inspection is necessary, body member 45 can be released simply by rotating body ring 18. Driven member 30 may then be removed by unscrewing it from the threaded end 27 of shaft 20. An outlet tube 50 and an inlet tube 52 are each attached to the exterior of the body members. Each tube has a central connection 53 and a tube locking ring 54 at each end. Tube locking rings 54 have internal threads that screw onto external threads on body connections 55. Each body connection 55 houses a ball valve 56 comprising an O-ring seal 57, a valve seat 58, and a valve ball 59. In the embodiment depicted, inlet tube 52 further includes a pair of mounts 60 for mounting the pump to a flat surface. The pump further includes a shuttle valve 65, which is secured to pump core 15 with two plastic screws 67. Shuttle valve 65 receives a supply of compressed air through an air inlet 68. As is known in the art, shuttle valve 65 switches the supply of compressed air alternately from one side of the pump to the other to drive the pump. The action of the pump can best be understood by referring to Fig. 2. The supply of compressed air will first be connected to pressure chamber 40 defined by the interior of driven member 30 on one side of the pump. Assume that the air pressure is applied first to the left driven member. As end cap 32 of driven member 30 is driven outward, the left bellows will expand and the right bellows will contract as the right driven member is pulled inward by pump shaft 20. Withdrawal of the right driven member from the interior of right body member 45 creates a vacuum within the pumping chamber 70 on the right side of the pump. Valve ball 59 on the upper right of the pump seals against valve seat 58 to close off outlet tube 50 from right pumping chamber 71. At the same time, pumped fluid is drawn from inlet tube 52 into the right pumping chamber 71 through the valve on the lower right side of the pump. When the left driven member is fully extended into left pumping chamber 72, the shuttle slides inside the shuttle valve thereby switching the supply of compressed air to right pressure chamber 40. Driven member 30 on the right side of the pump is pushed into right pumping chamber 71 simultaneously compressing the left driven member. The fluid in right pumping chamber 71 is pushed out into outlet tube 50 through the ball valve on the upper right side of the pump while the ball valve on the lower right closes off inlet tube 52. Simultaneously, a new volume of fluid is drawn from inlet tube 52 into left pumping chamber 72. Air in the left pressure chamber is exhausted out the back side of pump core 15. One or more mufflers 75 (Fig. 1) are typically used to control noise from compressed air exiting the back side of the pump. Pumping continues in this fashion with fluid being alternately drawn into and exhausted from the left and right pumping chambers in sequence. The dual chamber bellows pump described herein is superior to known dual diaphragm pumps in a number of important ways. First, one expansion of the bellows on the driven member pumps much more fluid than does a single flexure of a diaphragm used in a prior art pump of equivalent size. This means that, for a given flow rate, the reciprocation frequency of pump shaft 20 through pump core 15 can be correspondingly less. O-rings 22 (Fig. 2) around pump shaft 20 wear more slowly than in previous designs and less frequent maintenance is required. A corresponding decrease in wear is experienced by ball valves 56 and shuttle valve 65, which also reciprocate at a lower frequency. Additionally, pressure variation in the pumped fluid is of lower frequency and amplitude than in a diaphragm pump of similar capacity. Another important benefit is provided by the pump design described herein. The pump is constructed according to a simple design using a small number of easily assembled parts. Outlet and inlet tubes 50 and 52 including ball valves 56, body members 45, and driven members 30 can all be removed from pump core 15 without using tools. A screwdriver is the only tool needed to completely disassemble the pump. Assembly and disassembly of the pump is not complicated by large numbers of small clamps and fittings as in previous designs. Furthermore, the pump is manufactured entirely of corrosion-resistant plastics materials. As discussed above, this will be of paramount importance in highly demanding applications particularly in the semiconductor industry. In comparison with previous designs, no metal clamps are needed to secure the body members or inlet and outlet tubes to the pump--rotatable body rings 18 can be provided with large threads or an alternative fastening mechanism of sufficient strength. Similarly, large threads can be used on tube locking rings 54. In an exemplary embodiment, pump body members 45, inlet tube 52, and outlet tube 50 are formed of perfluoroalcoxy (PFA). Valve seats 58, valve balls 59, and driven members 30 are made of polytetrafluoroethylene (PTFE). Body rings 18, pump core 15, and back plates 25 are formed of polyvinylidene fluoride (PVDF). Pump shaft 20 is molded from polyetherketone (PEEK). Finally, the various O-rings 22, 38, 47, and 57 are formed from a fluorinated ethylene-propylene copolymer (FEP). Of course, a number of materials combining the desired corrosion resistance with sufficient mechanical strength and formability may be substituted for the exemplary materials described above. One embodiment of a pump according to the present invention has been described in considerable detail. However, modifications to this design may be made without departing from the principles of the invention as defined in the claims. In particular, it should be noted that the method of securing the body members to the pump core by means of rotatable body rings could find use even in a dual diaphragm pump.

Claims: A pump comprising a pump shaft (20), a pair of driven members (30) secured one to each end of the shaft (20), a pair of body members (45) disposed over the driven members (30) and each having an interior which, in combination with the associated driven member (30), defines a pumping chamber (70), and means for applying pressure alternately to the driven members (30), each driven member (30) includes an expandable bellows (36), characterised in that the pump is formed entirely of corrosion resistant plastics. A pump comprising a pump core (15), a pump shaft (20), a pair of driven members (30) secured one to each end of the shaft (20), a pair of body members (45) disposed over the driven members (30) and each having an interior which, in combination with the associated driven member (30), defines a pumping chamber (70), means for applying pressure alternately to the driven members (30), and a pair of body rings (18) in connection with said pump core (15) and rotatable between locked and unlocked positions, one securing each of the body members (45) to the pump characterised in that said body members (45) are manually releasable from the pump, without tools, by rotation of the associated body rings (18), further characterised in that the pump is entirely constructed of corrosion resistant plastics. A pump as claimed in claim 2, wherein each driven member (30), includes an expandable bellows (36). A pump according to claim 2 or claim 3, wherein each of the body members (45) is secured to the pump by a threaded connection between the body member (45) and one of the body rings (18). A pump according to any one of claims 1 to 4 wherein each of the driven members (30) is secured to the pump shaft (20) by a threaded connection between the driven member (30) and the associated end of the pump shaft (20). A pump according to any one of claims 1 to 5 and further comprising an outlet tube (50) and an inlet tube (52) in fluid communication with the interior of both of the body members (45), wherein each tube (50, 52) is secured to the exterior of both of the body members (45) by a pair of rotatable tube locking rings (54.) A pump according to claim 6, wherein the tubes (50, 52) are secured to the exterior of the body members (45) by threaded connections between the locking rings (54) and the body members (45). A pump according to any one of claims 1 to 7, wherein said plastics are organic polymers. A pump according to claim 8, wherein said plastics include fluorinated polymers. A pump according to claim 8 or claim 9, wherein the corrosion resistant materials are selected from the group consisting of PFA, PTFE, PVDF, PEEK, and FEP.

Inventors: CHEVALLIER YVES, CHEVALLIER, YVES
Applicants: ASTI S A E, ASTI S.A.E.
Application year: 1994
Main classification: F04B43
IPC codes: F04B15, F04B43